This invention relates to a digital circuit multiplexing equipment (DCME) device for use in assigning a plurality of input digital signals arranged in a plurality of input channels to a plurality of output channels, such as satellite channels, interexchange channels, or the like.
In general, telephone communication is carried out with a communication or telephone line occupied during the telephone communication. In this event, it is known in the art that an occupied time interval of the telephone line is longer than a time interval during which speech or voice energy is actually present in the telephone line and which may be called a speech time interval and that a ratio of the speech interval to the occupied time interval will be referred to as a speech activity. Practically, the speech activity is less than 40%, as well known in the art. This shows that any other speech communication may be assigned to or interpolated in the remaining time interval except the speech interval in a digital fashion. In this connection, the above-mentioned technique will be called a digital speech interpolation (DSI) technique. According to the digital speech interpolation technique, effective transmission can be carried out only during each speech interval alone.
Herein, inasmuch as each input speech signal is arranged within each of input communication channels in a digital fashion in the telephone communication and is assigned to each of output communication channels, the input speech signals can be transmitted through the number of the output communication channels that is smaller than the number of the input communication channels when the digital speech interpolation technique is used. As a result, it is possible to effectively utilize the output communication channels by the use of the digital speech interpolation technique. Practically, such a digital speech interpolation technique is utilized in a satellite communication system.
In the meanwhile, consideration has been made about applying the digital speech interpolation technique to a digital circuit multiplexing equipment (DCME) unit. Herein, various sorts of input information signals should be effectively multiplexed by the DCME unit. For example, the input information signals may include a variable length code subjected to high efficiency speech encoding, such as adaptive differential pulse code modulation (ADPCM), and a data signal of a bit rate of 64 Kbit/s. Such use of a DCME unit is helpful for effectively increasing a transmission capacity. However, a large size of hardware is necessary for multiplexing various sorts of input information signals by the DCME unit.